Method of Flocculation

Abstract

A coagulation treatment method for water to be treated that is capable of reducing the degree of inflow of micro flocs reaching a sand filtration layer while realizing a higher density and miniaturization of micro flocs and flocs in a state where the use of an inorganic coagulant is limited by dramatic improvement in residual percentage in a contact-media accumulation tank, based on obtaining a residual percentage (filtration rate) not less than 80% of flocs with particle diameters not less than 7.0 μm in a contact-media accumulation tank from a stage that the water to be treated starts to pass through by interposing the contact-media accumulation tank in a micro flocculation step and a sand filtration step, and filling flocs with particle diameters not less than 7.0 μm in advance at an inlet of the contact-media accumulation tank and/or the vicinity of the inlet.

1 . A coagulation treatment method for water to be treated, comprising:
 an inorganic coagulant injection step for injecting an inorganic coagulant into water to be treated;   a micro flocculation step for mixing and agitating the water to be treated into which the inorganic coagulant is injected in a rapid agitation tank to attain in advance micro-flocculation of fine suspended particles in the water to be treated; and   a sand filtration step at a final stage,   interposing a contact-media accumulation tank in which contact media capable of accelerating flocculation of micro flocs and trapping the micro flocs and flocs are accumulated between the micro flocculation step and the sand filtration step, and   filling in advance flocs including flocs with particle diameters not less than 7.0 μm at least one of:
 an inlet of the contact-media accumulation tank and 
 a vicinity of the inlet inside the contact-media accumulation tank, 
   
       a residual percentage (filtration rate) of flocs with particle diameters not less than 7.0 μm in the contact-media accumulation tank at a stage that the water to be treated starts to pass through the contact-media accumulation tank is set to be not less than 80%. 
     
     
         2 . The coagulation treatment method for water to be treated according to  claim 1 , further comprising the steps of:
 a flocculation step for accelerating flocculation by contact of the micro flocs with existing flocs and   a sedimentation separation step for separating the flocs by sedimentation   both interposed between the micro flocculation step and the sand filtration step, and   wherein the contact-media accumulation tank is provided at a stage at least one of before and after the flocculation step and the sedimentation separation step.   
     
     
         3 . The coagulation treatment method for water to be treated according to  claim 1 , further comprising the step of adopting, just after the micro flocculation step, a plurality of units of contact-media accumulation tanks. 
     
     
         4 . The coagulation treatment method for water to be treated according to  claim 1 , further comprising the step of providing, at a stage just after the micro flocculation step, next to the contact-media accumulation tank, a contact-media accumulation tank not filled with flocs including flocs with particle diameters not less than 7.0 μm at least at one of:
 the inlet and 
 the vicinity of the inlet. 
 
     
     
         5 . The coagulation treatment method for water to be treated according to  claim 1 , further comprising the step of providing, at a stage just before the sand filtration step, a contact-media accumulation tank in a basin positioned above a sand filtration layer and formed by pooling. 
     
     
         6 . The coagulation treatment method for water to be treated according to  claim 1 , wherein as the flocculation step and the sedimentation separation step, one of the following is adopted:
 a sludge blanket system, and   a system in which a sedimentation basin is subsequent to an agitation tank.   
     
     
         7 . The coagulation treatment method for water to be treated according to  claim 1 , wherein further comprising the step of causing water to be treated to flow from a lower side to an upper side in the contact-media accumulation tank. 
     
     
         8 . The coagulation treatment method for water to be treated according to  claim 1 , further comprising the step of adjusting, at a stage before the water to be treated flows into the contact-media accumulation tank, an injection amount of the inorganic coagulant so that turbidity becomes not more than 20 degrees. 
     
     
         9 . The coagulation treatment method for water to be treated according to  claim 1 , wherein
 in the micro flocculation step, further comprising the step of providing a rapid agitation tank divided into at least two compartments arranged in series so that the water to be treated can move sequentially, and   further comprising:
 a first coagulant injection step for injecting an inorganic coagulant into a whole or a part of the water to be treated at a stage leading to a first compartment of the micro flocculation step and 
 a second coagulant injection step for injecting an inorganic coagulant into a whole or a part of the water to be treated at a stage leading from a second compartment of the micro flocculation step to the flocculation step, and 
 adjusting injection amounts respectively in the first coagulant injection step and the second coagulant injection step. 
   
     
     
         10 . The coagulation treatment method for water to be treated according to  claim 1 , further comprising the step of using as an index for indicating a remaining amount of coagulants and agglomerates, an STR (Suction Time Ratio: an index indicated by Ts/Tv where distilled water equal in temperature and volume with water to be treated is used to suck the same filter paper at the same suction level and where the suction time of the water to be treated is given as Ts and that of the distilled water is given as Tv) of water to be treated at a stage that the micro flocculation step is completed is not more than 4.0. 
     
     
         11 . The coagulation treatment method for water to be treated according to  claim 1 , further comprising the step of re-injecting the coagulant into water to be treated flowing out from the contact-media accumulation tank and flowing in the sand filtration layer. 
     
     
         12 . The coagulation treatment method for water to be treated according to  claim 1 , wherein when filling in advance flocs including flocs with particle diameters not less than 7.0 μm at one of the inlet of the contact-media accumulation tank and the vicinity of the inlet inside the contact-media accumulation tank at a stage before water to be treated flows in, further comprising the steps of discharging an excess of the flocs from a discharge port positioned at an upper limit of the vicinity of the inlet, and closing a valve at the discharge port at the stage that the water to be treated flows in.